Friedel-Crafts alkylation product

Benzyl and allyl alcohols which can generate stabilized caibocations give Friedel-Crafts alkylation products with mild Lewis acid catalysts such as scandium triflate. ... 

Bromoadamantane and 1-bromoadamantane are reduced to adamantane in yields of 84% and 79%, respectively, when treated with triethylsilane and catalytic amounts of aluminum chloride.186 Similar treatment of benzhydryl chloride and exo-2-bromonorbomane gives the related hydrocarbons in yields of 100% and 96%, respectively.186 In contrast, 2-bromo-l-phenylpropane gives only a 43% yield of 1-phenylpropane the remainder consists of Friedel-Crafts alkylation products.186 Some alkyl halides resist reduction by this method, even when forcing conditions are employed. These include p-nitrobenzyl bromide, 3-bromopropanenitrile, and 5-bromopentanenitrile.186... 

Friedel-Crafts alkylation product is more reactive does not work for strongly deactivated rings rearrangements are common can also use acid plus alkene or alcohol to generate electrophile... 

The diastereoselective [4 + 3] cycloaddition between 2,5-disubstituted furans and vinylthionium ions was achieved (140L4476). The vinylthio-nium ion was generated either from a ort/io-phenylethynylbenzoyl allylic ester in the presence of a gold catalyst or from the allylic alcohol with a Bronsted acid. However, using 2-substituted furans led predominantly to the formation of Friedel-Crafts alkylated products. 

The catalytic enantioselective FriedelYIlrafts alkylation reaction of indoles (502) with y,5-unsaturated p-keto phosphonates (503), under the mild reaction conditions, promoted by air and moisture-stable chiral palladium diphosphine complexes (505) at room temperature, afforded the corresponding Friedel-Crafts alkylation products (504) with excellent enantioselectivities (up to 99% ee) (Scheme 125). ... 

Because acylation of an aromatic ring can be accomplished without rearrangement it is frequently used as the first step m a procedure for the alkylation of aromatic compounds by acylation-reduction As we saw m Section 12 6 Friedel-Crafts alkylation of ben zene with primary alkyl halides normally yields products having rearranged alkyl groups as substituents When a compound of the type ArCH2R is desired a two step sequence IS used m which the first step is a Friedel-Crafts acylation... 

Haloall lation. Haloalkyl groups can be introduced directiy by processes similar to Friedel-Crafts alkylation into aromatic and, to some extent, ahphatic compounds. Because halo alkylations involve bi- or polyfunctional alkylating agents, they must be performed under conditions that promote the initial halo alkylation but not, to any substantial degree, subsequent further alkylations with the initially formed haloalkylated products. 

Cumene. Cumene (qv) is produced by Friedel-Crafts alkylation of benzene by propylene (103,104). The main appHcation of cumene is the production of phenol (qv) and by-product acetone (qv). Minor amounts are used in gasoline blending (105). 

Short-chain alkylated biphenyls are the principal biphenyl derivatives in commercial use. They are generally produced by Hquid-phase Friedel-Crafts alkylation of biphenyl with ethylene, propylene, or mixed butenes. A series of mixed ethylated biphenyl heat-transfer fluids (trademarked Therm S-600, 700, 800) is marketed by Nippon Steel. A mixed diethylbenzene—ethylbiphenyl heat-transfer fluid is also available from Dow (63). Monoisopropylbiphenyl [25640-78-2] largely as a mixture of meta- and para-isomers is produced by Koch Chemical Co. Monoisopropylbiphenyl (MIPB) was selected by Westinghouse (64,65) as a PCB replacement in capacitors and this is its primary appHcation today. For a time MIPB was also employed as a PCB replacement in pressure sensitive copy paper, but this outlet has since given way to other dye solvents. A similar product consisting of a mixture of j -butylbiphenyl isomers [38784-93-9] (66) is currently the favored dye solvent for pressure sensitive copy paper (67) manufactured in the United States. 

Steric effects play a major role in determining the ortho para ratio in Friedel-Crafts alkylations. The amount of ortho substitution of toluene decreases as the size of the entering alkyl group increases along the series methyl, ethyl, /-propyl. No ortho product is found when the entering group is /-butyl. ... 

Of the many methods which have been published so far for the substitution of existing crowns, probably the most straightforward are Friedel-Crafts alkylation or acylation reactions. Cygan, Biernat and Chadzynski have reported the successful di-t-butylation of dibenzo-24-crown-8 using t-butanol as alkylating agent s . The crown was heated at 100° for 4 h in the presence of excess t-butanol and 85% phosphoric acid. The product was obtained as a crystalline (mp 52—74°) solid in 93% yield. The alkylated crowns are presumably a mixture of isomers substituted once in each ring as illustrated in Eq. (3.14). 

Drawbacks as known from the Friedel-Crafts alkylation are not found for the Friedel-Crafts acylation. In some cases a decarbonylation may be observed as a side-reaction, e.g. if loss of CO from the acylium ion will lead to a stable carbenium species 8. The reaction product of the attempted acylation will then be rather an alkylated aromatic compound 9 ... 

The intramolecular variant of the Friedel-Crafts alkylation is also synthetically useful, especially for the closure of six-membered rings, e.g. the synthesis of tetraline 8 but five- and seven-membered ring products are also accessible ... 

It should be noted that Scheme 5.1-44 shows idealized Friedel-Crafts allcylation reactions. In practice, there are a number of problems associated with the reaction. These include polyalkylation reactions, since the products of a Friedel-Crafts alkylation reaction are often more reactive than the starting material. Also, isomerization and rearrangement reactions can occur, and can result in a large number of products [74, 75]. The mechanism of Friedel-Crafts reactions is not straightforward, and it is possible to propose two or more different mechanisms for a given reaction. Examples of the typical processes occurring in a Friedel-Crafts alkylation reaction are given in Scheme 5.1-45 for the reaction between 1-chloropropane and benzene. 

Ualike the multiple substitutions that often occur in Friedel-Crafts alkylations, acylations never occur more than once on a ring because the product acyl-benzene is less reactive than the nonacylated starting material. We ll account for this reactivity difference in the next section. 

For example /-butyl phenyl ether with aluminium chloride forms para-t-butyl phenol155. Often the de-alkylated phenol is also formed in considerable quantity. The reaction formally resembles the Fries and Claisen rearrangements. Like the Fries rearrangement the question of inter- or intramolecularity has not been settled, although may experiments based on cross-over studies156, the use of optically active ethers157 and comparison with product distribution from Friedel-Crafts alkylation of phenols158 have been carried out with this purpose in view. 

Mohanty et al. were the first to introduce pendent r-butyl groups in die polymer backbones. The resulting material was quite soluble in aprotic dipolar solvents.83 The PEEK precursors were prepared under a mild reaction condition at 170°C. The polymer precursor can be converted to PEEK in die presence of Lewis acid catalyst A1C13 via a retro Friedel-Crafts alkylation. Approximately 50% of die rerr-butyl substitutes were removed due to die insolubility of the product in die solvent used. Later, Risse et al. showed diat complete cleavage of f< rf-butyl substitutes could be achieved using a strong Lewis acid CF3SO3H as both die catalyst and the reaction medium (Scheme 6.15).84... 

In this section, the reactivities of organosilicon compounds for the Friedel-Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions will be discus.sed, along with the orientation and isomer distribution in the products and associated problems such as the decomposition of chloroalkylsilanes to chlorosilanes.. Side reactions such as transalkylation and reorientation of alkylated products will also be mentioned, and the insertion reaction of allylsilylation and other related reactions will be explained. 

Vinylchlorosilanes react with aromatic compounds in the presence of Lewis acid to give the alkylation products 2-(chlorosilyl)ethylarenes. In the Friedel-Crafts alkylation of aromatic compounds, the reactivity of vinylchlorosilanes is slightly lower than that of allylchlorosilanes.Friedel-Crafts alkylation of benzene derivatives with vinylsilanes to give 2-(chlorosilyl)ethylarenes was first reported by the Andrianov group (Eq. (5))." The reactivity of vinylsilanes in the... 

Dichloroalkyl)chlorosilanes undergo the Friedel-Crafts alkylation type reaction with biphenyl in the presence of aluniinurn chloride catalyst to afford 9-((chlorosilyl)alkyl)fluorenes through two step reactions (Eq. (16)). The results obtained from the alkylation of biphenyl and the cyclization reaction to 5-membered-ring product are summarized in Table XIIE... 

The mechanism for the production of 9-((chlorosilyl)alkyl)(luorenes from the Friedel-Crafts alkylation reaction of biphenyl with (l,2-dichloroethyl)silane in the presence of aluminum chloride as catalyst is outlined in Scheme 4. At the beginning stage of the reaction, one of two C—Cl bondsof (1,2-dichloroethyl)silane (CICH2—CICH—SiXi) interacts with aluminum chloride catalyst to give intermediate 1 (a polar +C-CI - ( +C-C1—Al CI3) or a carbocation C AICU ... 

Furthermore, Jana et al. developed a FeCl3-catalyzed C3-selective Friedel-Crafts alkylation of indoles, using allylic, benzylic, and propargylic alcohols in nitromethane as solvent at room temperature. This method can also be used for the alkylation of pyrrole (Scheme 4). The reactions were complete within 2-3 h without the need of an inert gas atmosphere leading to the C-3-substitution product exclusively in moderate to good yields [20]. 

Friedel-Crafts alkylations are among the most important reactions in organic synthesis. Solid acid catalysts have advantages in ease of product recovery, reduced waste streams, and reduction in corrosion and toxicity. In the past, people have used (pillared) clays (18), heteropolyacids (19) and zeohtes (20) for Friedel-Craft alkylations, with mixed success. Problems included poor catalyst stabihty and low activity. Benzylation of benzene using benzyl chloride is interesting for the preparation of substitutes of polychlorobenzene in the apphcation of dielectrics. The performance of Si-TUD-1 with different heteroatoms (Fe, Ga, Sn and Ti) was evaluated, and different levels of Fe inside Si-TUD-1 (denoted Fei, Fe2, Fes and Feio) were evaluated (21). The synthesis procedure of these materials was described in detail elsewhere (22). 

Friedel-Crafts alkylation can occur intramolecularly to form a fused ring. Intramolecular Friedel-Crafts reactions provide an important method for constructing polycyclic hydrocarbon frameworks. It is somewhat easier to form six-membered than five-membered rings in such reactions. Thus, whereas 4-phenyl-1-butanol gives a 50% yield of a cyclized product in phosphoric acid, 3-phenyl-1-propanol is mainly dehydrated to alkenes.43... 

In all that has gone before a tacit assumption has been made that the proportions of alternative products formed in a reaction, e.g. o-, m- and p-isomers, are determined by their relative rates of formation, i.e. that the control is kinetic (p. 42). This is not, however, always what is observed in practice thus in the Friedel-Crafts alkylation of methyl-benzene (Me o-/p-directing) with benzyl bromide and GaBr3 (as Lewis acid catalyst) at 25°, the isomer distribution is found to be ... 

The C2-symmetric bifunctional tridentate bis(thiazoline) 222 has been shown to promote the zinc(II)-catalyzed asymmetric Michael addition of nitroalkanes to nitroalkenes in high enantioselectivity <06JA7418>. The corresponding bis(oxazoline) ligand provides comparable enantioselectivity but higher product yield. The same bis(thiazoline) ligand has also been evaluated in the enantioselective Friedel-Crafts alkylation of indoles, but the enantioselectivity is moderate <06OL2115>. 

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